<style type="text/css">
  .main
  {
    background-color: lightgreen;
    /*border: solid 2px black;*/
  }
  .inline-block
  {
    display: inline-block;
    background-color: lightcyan;
    border: solid 1px black;
    font-size: 2em;
  }
</style>

<span class="main">
	Lorem
	<div class="inline-block">a<br>b</div>
</span>